Sensitive loads such as computers, data processing equipment and medical equipment must be protected from sudden changes of the line voltage and/or frequency. Such sensitive or critical loads also include hospitals, clinics, life support system, military installations, land, air and sea borne traffic control installations, remote systems such as those controlled by the armed forces, weather monitoring systems, critical manufacturing processes, nuclear facilities, large banking facilities, computer installations, large building elevators, emergency lighting and other loads where loss of power can be threatening to human life or property. It is desirable to limit undesirable electrical power instabilities coming from the electric utility lines by using backup power sources.
British patent 1,309,858 discloses an uninterrupted power supply for ensuring that uninterrupted power is supplied to a load. This supply provides partial compensation to a voltage drop by connecting an auxiliary power supply to the load via a secondary winding of a transformer, the primary winding of which is connected to a choke located between the main power supply and the supply. The use of a transformer disadvantageously makes the system expensive.
Many of the current uninterrupted power supplies may accomplish the required protection using a rotating flywheel disadvantageously having large weight. Depending upon rotating flywheel mass requirements, the flywheel may be a separate structure or incorporated into an arrangement of the a motor, shaft, or rotor. For sensitive or critical loads where even a small change in frequency can cause problems, flywheel size requirement may become impractical. The flywheel large spinning mass also creates problems in startup and performance when acceleration or deceleration of the spinning mass is required.
EP 69568 discloses an uninterrupted power supply using a high frequency method wherein a high frequency alternating current (AC) power generator drives a small, high speed motor and flywheel both located in a sealed chamber. This approach is relatively expensive due to the use of an additional high frequency generator. Maintaining electric power frequency and phase within tolerances for sensitive or critical loads has also been a problem. Apparatus, which modifies frequency and other complex devices, have been used.
U.S. Pat. Nos. 4,827,152, 5,311,062 and 5,434,454 disclose uninterrupted power supplies having high pressurized hydraulic systems. These systems are unreliable since the high pressure piping included in these systems can burst. Furthermore, these systems do not provide the required frequency needed for such systems due to the need to accelerate the hydraulic motor at the outage instant.
There exists a need for a simpler and more effective power backup system which can substantially instantaneously respond to utility failures of the line power without the disadvantages of heavy flywheels or high pressurized hydraulics, and frequent maintenance. These and other disadvantages are solved or reduce using the present invention.